Effects and possible mechanisms of dissolved organic matter originated from cattle manure on adsorption of cadmium by periphyton

Dissolved organic matter (DOM) originated from livestock manure often co-exists with cadmium ion (Cd) in livestock effluent. However, the effects of DOM on removal efficiency of Cd by adsorbent remain unknown. This study investigated the effects of DOM originated from cattle manure on adsorption behaviors of Cd by periphyton, and the possible mechanisms were also explored through desorption analyses, Fourier transform infrared spectroscopy (FTIR) determination, and histochemical staining. The adsorption kinetics and isotherm of Cd by periphyton could be explained by pseudo-second-order model and Freundlich model, respectively. DOM addition did not change the adsorption kinetics and isotherm of periphyton toward Cd, but it decreased the adsorption capacity of Cd by periphyton. Ion exchange and complexation were the main binding forces for the adsorption of Cd by periphyton, while the adsorption of Cd by DOM mainly through complexation. Amide and hydroxyl in the DOM were involved in its adsorption toward Cd, and may contribute to the competition for Cd with periphyton. Thus, the decrease of DOM concentration in livestock effluent is helpful to remove Cd by periphyton adsorption.